By: Patrick Brown, 2nd year PhD candidate in the Biomedical Sciences Graduate Program
Due to hit shows like CSI and The Big Bang Theory as well as an increase in news reporting, there is a growing interest in the various fields of biological science. As a scientist, I encourage everyone to learn more about the processes and molecules that make life possible. Unfortunately, it can be a daunting task for someone unfamiliar with science jargon to get simple questions answered or learn more about a topic of interest to them. So where to begin? Let’s start with the building block of life: DNA.
The central dogma of molecular biology is that DNA becomes mRNA, which is coded into protein. At its simplest form, deoxyribonucleic acid (DNA) is comprised of four bases – adenine, thymine, cytosine, and guanine. The ordering of these bases in specific arrangements forms genes.
One gene can contain tens of thousands of bases, and the entire collection of human genes (known as the human genome) contains approximately 3 billion bases! Consequently, there are many genes in the human genome and each gene typically can be converted into one type of protein. Many different proteins are found throughout the cell where they perform important functions. But how is this genetic code converted into something useful?
DNA is converted into protein using a molecule called messenger ribonucleic acid (mRNA). DNA is a double-stranded molecule and is very stable. It is excellent for storing genetic information long periods of time, but it can difficult to access when quick production of protein is needed. DNA is converted to mRNA in a process called transcription. Once an mRNA strand is transcribed, it can be converted into a protein. mRNA is very similar to DNA because it too contains four bases, but unlike DNA it is single-stranded and less stable. The single-stranded nature of mRNA allows proteins to be synthesized from it relatively quickly.
Proteins are relatively large compared to a DNA or mRNA base and are comprised of many amino acids. There are 21 amino acids, and they are produced in our body from the various foods and supplements we ingest. When the cell wants to make a protein, cellular components attach to mRNA and “decode” it. The coding system is read three bases of mRNA at a time. Every three-base sequence corresponds to a specific amino acid. As the machinery “walks” along an mRNA strand, amino acids are strung together until the full protein has been completed. This process is called translation. At this point the protein can go and perform functions in the cell.
This stepwise process from DNA to protein is needed for several reasons. First, while making protein requires much energy, degrading it is also inefficient. Additionally, it is not necessary for one cell to produce every protein that your DNA encodes.
Differential protein expression allows cells throughout your body to perform different functions. For example, pancreatic cells secrete insulin, but nerve, skin, and blood cells cannot. How does the body choose which genes are expressed in which cells? This is partly controlled by a process called epigenetics, which will be the topic of my next entry.
Patrick Brown is a 2nd year PhD candidate in the Biomedical Sciences Graduate Program. He works in Dr. Colin Barnstable’s lab where he studies the modulation of the transcription factor STAT3 in retinal development. In his free time he enjoys exercising, wine tasting, and wine making.